Can't you just decline the dance in the first place?
Yes, you can but why would you?
It begins very innocently (plus, my character is already heavily involved with Astarion, with no even hints of any other romances). There are three interactions before the actual dance: 1. curiosity or 2 heavy insults to Wyll. The choice is clear. 2. If you go with the first option, again, curious questions like "but there is no music", "I am not interested" or insult him again. Once again - why stop? 3. Say, you are still curious you have two choices: "let's dance" or "I should call it a day". Why would I stop at this point?
Sure, he does smile all the way and we can interpret it as a hint but considering everything above...
You can also stop when he says something about getting more intimate;
No, you can not!
With Gale (now) you can do magic and still get very clear choice between "Continue. It is a perfect night to get intimate" and "Let's call it a day". With Wyll, once you agree to the dance, this is it. You have three options: "Take a bow", "Smile nervously", and "It was not hard" - all three lead to him declaring "Now let's get to the intimate part".
Larian fixed Gale's part but forgot about Wyll's. That's why I remember Jacob.
